Drawn and ironed (D & L) cans are currently in wide use as containers for beverages. These D & I cans are manufactured by the following procedure: an aluminum or tinplate workpiece is blanked out, drawn and ironed, and after the open end portion is trimmed and otherwise worked, the can is transported on a net conveyor with the open end facing down while it is sprayed with an upward and downward shower of aqueous degreasing agent for removing the coolant (lubricant) that has been deposited on the surfaces of the can during ironing, and with an upward and downward shower of aqueous chemical to provide a corrosion-resistant surface and improved paint adhesion. These procedures of degreasing and chemical surface treatment consist of the following steps: (preliminary decreasing).fwdarw.degreasing.fwdarw.blowing off.fwdarw.washing with water.fwdarw.blowing off.fwdarw.chemical surface treatment.fwdarw.blowing off.fwdarw.washing with water.fwdarw.blowing off.fwdarw.washing with deionized water.fwdarw.blowing off.fwdarw.drying. The "blowing off" means blowing the liquid treating agent off the bottom of the can with compressed air. After drying, the can is forwarded to coating and printing steps.
The treating method outlined above is employed in many commercial can making factories. A compact apparatus for surface treatment that achieves degreasing in a shorter period of time is described in Japanese Laid-open Patent Publication No. 158489/75 (corresponding to U.S. Pat. No. 4,026,311). A side elevational view of the apparatus is represented in the accompanying FIG. 1. The apparatus comprises a base plate 1, a cylindrical core 2 extending vertically from the base plate 1, and a shell 3 extending vertically from the base plate 1 and being positioned concentrically with the core 2 to cover it. The apparatus also includes a first channel 4 for discharging or introducing the treating fluid which penetrates the base plate 1 and also penetrates the core 2 along its central axis, a second channel 6 for introducing or discharging the treating fluid that penetrates the center of the top wall 5 of the shell 3, and a plurality of projecting fins 8 that are formed around the lower end 7 of the core 2 at a suitable interval and which fit the open end 20 of the can to be treated. The base plate 1, core 2 and the shell 3 form a cavity 15. In FIG. 1, the can is shown generally by the phantom line A as if it were put in the cavity 15. The shape produced by the inner surface 9 of the can and the outer surface 10 of the core 2 is similar to that produced by the outer surface 11 of the can and the inner surface 12 of the shell 3, and the gap l between the surfaces 9 and 10 as well as the gap l' between the surfaces 11 and 12 is very small.
The inner and outer surfaces of the can are degreased in the apparatus of FIG. 1 as follows: first, the can A is positioned in such a manner that the inner surface of the open end 20 of the can fits the projecting fins 8 and the flat portion 21 of the open end is in contact with the upper surface 13 of the base plate; then, a degreasing fluid made of an organic solvent (e.g. trichloroethylene) is poured through the second channel 6; the fluid flows down the gap l' between the outer surface 11 of the can and the inner surface 12 of the shell 3, goes through slots 14 formed between each fin 8, goes up the gap l between the inner surface 9 of the can and the outer surface 10 of the core 2, and goes out of the apparatus through the first channel 4. The above sequence enables both inner and outer surfaces 9 and 11 of the can to be degreased. Subsequently, the remaining degreasing fluid is removed by the following procedure: rinsing water is poured through the second channel 6; the water flows down the gap l' between the outer surface 11 of the can and the inner surface 12 of the shell 3, goes through the slots 14, goes up the gap l between the inner surface 9 of the can and the outer surface 10 of the core 2, and goes out of the apparatus through the first channel 4. This sequence enables the degreasing fluid to be washed away from both inner and outer surfaces 9 and 11 of the can. Subsequently, heated air is supplied into the cavity through the first channel 4 to dry both the inner and outer surfaces 9 and 11 of the can. The above degreasing and drying procedures are followed by the chemical surface treatment which consists, as described before, of application of a chemical.fwdarw.blowing off.fwdarw.washing with water.fwdarw.blowing off.fwdarw.washing with deionized water.fwdarw.blowing off.fwdarw.drying. We presume the advantage of degreasing the can with trichloroethylene or other organic solvents in the small cavity in the apparatus of FIG. 1 are that degreasing can be accomplished in a shorter period with an apparatus smaller in size than the method of degreasing cans that are being transported on a net conveyor. As already mentioned, the degreased can is subjected to chemical surface treatment or coating procedures to form a corrosion-resistant protective layer, and the industry has need for further reducing the overall period of surface treatments and the energy spent in the treatments.